1. Field of the Invention
This invention relates to an image size enlarging and reducing method and an apparatus for carrying out the method. This invention particularly relates to an image size enlarging and reducing method, wherein a plurality of images, which should satisfy different requirements for sharpness, are combined with one another, and wherein a composed image having a desired size is thereby obtained, and an apparatus for carrying out the method.
2. Description of the Prior Art
Techniques for photoelectrically reading out a radiation image, which has been recorded on a photographic film, in order to obtain an image signal, carrying out appropriate image processing on the image signal, and then reproducing a visible image by use of the processed image signal have heretofore been known in various fields.
Also, it has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a medical radiation image of an object, such as a human body, is recorded on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet, on which the radiation image has been stored, is then exposed to stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal is then processed and used for the reproduction of the radiation image of the object as a visible image on a recording material, such as photographic material, or on a display device, such as a cathode ray tube (CRT) display device.
The visible image for diagnosis, which is reproduced from an image signal obtained in the manner described above, is often used as a composed image, which is obtained by combining at least two different images with each other. For example, an image of a human body and a character image representing the date, on which the image of the human body was recorded, the characteristics of the recorded image of the human body, or the like, may be combined with each other. Also, a plurality of images of a portion of a human body, which were recorded from various different directions, may be arrayed in a composed image. Further, images of a plurality of related portions of a human body may be arrayed in a composed image. In order for such a composed image to be obtained, techniques have heretofore been employed, wherein a single predetermined process for enlarging or reducing the image size is selected previously, the sizes of the images subjected to the image composition are enlarged or reduced with the image size enlarging or reducing process in order to match the image sizes, and the images are then combined with one another. When necessary, the size of the thus obtained composed image is then enlarged or reduced.
Ordinarily, the enlargement or reduction of the image size is carried out by making various calculations on a first image signal, thereby obtaining a second image signal suitable for reproducing an image of a desired size, and reproducing a visible image from the second image signal. In such cases, the sharpness of the reproduced image depends markedly upon the process for obtaining the second image signal. Therefore, when the image size is enlarged or reduced, an appropriate image size enlarging or reducing process should preferably be employed in accordance with the level of sharpness required of the image. In particular, an interpolating operation process, which is employed for the enlargement of the image size, has a large influence upon the image quality of the image obtained from the image size enlargement. Therefore, an appropriate interpolating operation process should preferably be employed in accordance with the level of sharpness required of the image. The applicant has proposed various interpolating operation processes in, for example, U.S. Pat. No. 5,048,105, EP 753 828 A2 and Japanese Unexamined Patent Publication No. 9(1997)-50516.
However, in cases where the image size enlargement or reduction is carried out on a plurality of images of different kinds, the level of sharpness required of the image varies for different images. Therefore, with the conventional technique, wherein the sizes of the images are enlarged or reduced with a single selected image size enlarging or reducing process, the selected image size enlarging or reducing process cannot satisfy the sharpness requirements of all images. As a result, the problems occur in that an image, which has low image quality and does not satisfy the sharpness requirement, is obtained from the image size enlargement or reduction. For example, in cases where a character image, which should have a high level of sharpness, and an image of a human body, which should be smooth, are enlarged or reduced, if an image size enlarging or reducing process appropriate for the character image is selected, the level of sharpness of the image of the human body will also become high. If an image size enlarging or reducing process appropriate for the image of the human body is selected, the character image will become unsharp.